Purpose: We evaluated and optimized the detection of cancer by prostate biopsies. We developed a stochastic computer simulation model of ultrasound guided biopsies using mathematically reconstructed radical prostatectomy specimens. Use of this technique allows rapid evaluation of a variety of factors for their effect on prostate biopsy results. We used this model to analyze the effectiveness of sextant biopsies, which have been widely adopted in clinical practice. We also analyzed other biopsy schemes.
Materials and methods: A total of 607 tumor foci from 180 serially sectioned whole mount radical prostatectomy specimens was mapped and digitized. The cancers had been clinically diagnosed by a variety of biopsy strategies. Simulated parasagittal sextant biopsies were performed for each case. Forty simulation runs (each consisting of a set of 6 biopsies) were performed for each prostate, with realistic random variations in sextant biopsy localization programmed in each run. Cancer detection by biopsy was considered reliable if 90% of the simulation runs for each prostate were positive for cancer. A summary algorithm was used to map the tumor foci.
Results: Simulation of sextant biopsies demonstrated reliably detected cancer in only 107 of 147 patients (73%) in whom total tumor volume was greater than 0.5 cc. There was little correlation between total length of cancer in biopsy cores and tumor volume. Change of biopsy angle from 30 to 45 degrees did not result in significantly increased detection rates. Similarly, placing all biopsies more laterally did not increase overall detection rates. When we mapped tumor foci from the 40 cases in which sextant biopsies did not reliably detect tumor, we found that the foci were distributed in areas not biopsied by the sextant method, that is the transition zone, midline peripheral zone and inferior portion of the anterior horn of the peripheral zone. A 10-core biopsy scheme incorporating these areas as well as the posterolateral prostate reliably detected cancer in 141 of 147 patients (96%) with total tumor volumes greater than 0.5 cc.
Conclusions: Prostate cancer of significant volume can be present in areas not sampled by standard sextant biopsies. Biopsies of the transition zone, midline peripheral zone and inferior portion of the anterior horn of the peripheral zone should be considered for re-biopsy strategy after negative sextant biopsies. Sampling of these additional areas also can be incorporated in an initial biopsy scheme to increase overall initial rates of detection of prostate cancer.